1. Field of the Invention
The present invention relates generally to modulating circuitry. In particular, the present invention to an electronics circuit for modulating a sinusoidal waveform signal using digital pulse shaping.
2. Description of the Prior Art
Communications systems have evolved over the years to utilize numerous modulation techniques for modulation a carrier signal. These modulation techniques range from amplitude to frequency and phase modulation.
The transmission of digital data over communication circuits is an important aspect of many modern electronic communication systems. These systems include computers, data processing equipment, modems and many other devices which must frequently be interconnected over existing voice grade communication facilities such as telephone lines, satellite links and the like. However, the transmission characteristics of existing voice grade communication facilities are often not suitable for the direct transmission of the signals in a form most efficiently processed by these modern electronic communication systems. For example, high frequency components of digital data signals are beyond the transmission capability of a number of existing voice grade communication facilities. Thus, there arises a need for converting the binary data signal which is most efficiently used by these electronic systems into a signal that is compatible with existing transmission systems.
There have been developed over the years many modulation techniques for the efficient transmission of digital data over existing transmission systems. One modulation technique for the transmission of digital data that has found wide spread acceptance is frequency shift key (FSK) wherein a number of signals, usually two when a binary system is used, having separate discrete audio frequencies compatible with the transmission are each assigned a separate, different symbol identification portion of the data signal. For example, in a mark-space data signal, the mark is assigned a first frequency while the space is assigned the second frequency. In these FSK systems the frequency of the signal to be transmitted is shifted from the first frequency to the second frequency as a function of the mark and space symbol identification in the data signal.
When high frequency and radio frequency signals are used to transmit digital data signals frequency shift keying is employed to shift a continuous-running carrier in frequency between two closely spaced frequencies according to the ones and zeros being transmitted with 850 hertz of shift being a typical value. The use of frequency shift keying to transmit digital data is extremely efficient and effective in the presence of large signal fading from changing propagation conditions.
While there are many devices in the prior art to shift a continuous-running carrier in frequency between two closely spaced frequencies, none of these prior art devices allow the user to change the two closely spaced frequencies of the continuous carrier by using a personal computer or the like. In addition, it would be very desirable to allow the user of a system for frequency shift keying a continuous-running carrier to efficiently trouble shot the system through use a personnel computer.